1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing roll film. More specifically, the invention relates to a film cassette that is capable of automatically advancing a non-protruding film leader to the exterior of the cassette shell responsive to unwinding rotation of a film spool inside the shell.
2. Description of the Prior Art
In conventional 35 mm film manufacturers' cassettes, such as manufactured by Eastman Kodak Co. and Fuji Photo Film Co. Ltd., the filmstrip is wound on a flanged spool which is rotatably supported within a cylindrical shell. A leading or forward-most section of the filmstrip approximately 21/3 inches long, commonly referred to as a "film leader", normally protrudes from a light-trapped slit or mouth of the cassette shell. One end of the spool has a short axial extension which projects from the shell, enabling the spool to be turned by hand. If the spool is initially rotated in an unwinding direction, the film roll inside the shell will tend to expand radially since the inner end of the filmstrip is attached to the spool, and the fogged leader section protruding from the slit will remain stationary. The film roll can expand radially until a firm non-slipping relation is established between its outermost convolution and the inner curved wall of the shell. Once this non-slipping relation exists, there is a binding effect between the film roll and the shell which prevents further rotation of the spool in the unwinding direction. Thus, rotation of the spool in the unwinding direction cannot serve to advance the filmstrip out of the shell, and it is necessary in the typical 35 mm camera to engage the protruding leader section to draw the filmstrip out of the shell.
A 35 mm film cassette has been proposed which, unlike conventional film cassettes, can be operated to automatically advance a film leader out of the cassette shell by rotating the film spool in the unwinding direction. The film leader originally is located entirely inside the cassette shell. Specifically, in U.S. Pat. No. 4,423,943, granted Jan. 3, 1984, there is disclosed a film cassette wherein the outermost convolution of the film roll wound on the film spool is radially constrained by respective circumferential lips of two axially spaced flanges of the spool to prevent the outermost convolution from contacting an inner curved wall of the cassette shell. The trailing end of the filmstrip is secured to the film spool, and the forward or leading end of the filmstrip is slightly tapered purportedly to allow it to freely extend from between the circumferential lips and rest against the shell wall at a location inwardly of a non-lighttight film passageway to the outside of the cassette shell. During initial unwinding rotation of the film spool, the leading end of the filmstrip is advanced along the shell wall until it reaches an inner entrance to the film passageway. Then, it is advanced into and through the film passageway to the exterior of the cassette shell. The Passageway has a width that is less than the width of the filmstrip, thus resulting in the filmstrip being transversely bowed as it is uncoiled from the film spool, and thereby facilitating movement of the film edges under the circumferential lips of the flanges. However, severe transverse bowing of the filmstrip in order to move its longitudinal edges under the circumferential lips of the flanges may damage the filmstrip.
Like the type of film cassette disclosed in U.S. Pat. No. 4,423,943, commonly assigned U.S. Pat. No. 4,883,235 granted Nov. 28, 1989, discloses a film cassette that is capable of automatically advancing a non-protruding film leader to the exterior of the cassette shell in response to rotation of the film spool in the unwinding direction. Specifically, there is disclosed a film cassette wherein a film spool is supported for rotation in an unwinding direction inside a cassette shell, a convoluted film roll whose outermost convolution is a film leader is coiled in the unwinding direction about the spool, a pair of flanges are coaxially arranged along the spool to normally radially confine the film roll coiled about the spool, and a film stripper is located substantially adjacent a passageway to the exterior of the shell to be received between a leading edge portion of the film leader and a next-inward convolution of the film roll responsive to rotation of the spool in the unwinding direction to divert the leading edge portion to between a pair of light-trapping plush pads spaced opposite each other in the passageway. If the film roll has been stored on the spool for an unduly long time, e.g. 10 years, it may develop what is commonly referred to as a "core set". The core set, in essence, manifests itself as a lack of resistance of the film roll to being curled inward about the spool. Consequently, when the spool is rotated in the unwinding direction to move the leading edge portion of the film leader over the stripper, the leading edge portion (due to the leader's inward curl) may fall into a space between the stripper and one of the plush pads once the leading edge portion is advanced beyond the stripper. Since the film leader has a core set, it might remain in the space and cause a film jam inside the cassette shell.